Werlaid sheet



March 3, 1964 H FISH, JR

OF STAPLE FIBERS AND FIBRIDS Filed Dec. 5, 1960 F. APPARATUS FOR FORMING A WATERLAID SHEET 2 Sheets-Sheet l STAPLE STOCK G 1 SUPPLY TAIIII FI'BRID sTocR HEAD SUPPLY REFIIIER 7H RIRER MIXER BOX RRooucII DRYER I'IET FOURDRIIIIER REEL ROLLS PRESS MACHINE I I l I I l I I i I l l l I F BROKE IsLIIsRER l SUSPENDING LIQUID SUPPLY FLOYD HAMILTON FISH, JR.

March 3-, 1964 s JR 3,123,520

APPARATUS FOR FORMING A WATERLAID SHEET 0F STAPLE FIBERS AND FIBRIDS 2 Sheets-Sheet 2 Filed Dec. 5, 1960 FIG. 3

Fl G. 4

INVENTOR FLOYD HAMILTON FISH, JR.

ATTORNEY United States Patent 3,123,520 APPARATUS FOR FORMING A WATERLAID SHEET OF STAPLE FEBERS AND FIBRIDS Floyd Hamilton Fish, In, Wilmington, DeL, assignor to E. I. du Pont de Nemours and Company, Wilmington,

Del., a corporation of Delaware Fiied Dec. 5, 1960, Ser. No. 73,955 6 Claims. (Cl. 162-342) The present invention relates to a novel and useful apparatus for the formation of a sheet-like structure. More specifically, it relates to a headbox which is particularly adapted for forming such a structure on a papermaking machine.

It is an object of the present invention therefore to provide a novel headbox for a papermaking machine which is particularly useful in the formation of such a non-woven, sheet-like structure. Other objects will become apparent from the descriptions, the drawings and the claims.

In accordance with the present invention, a headbox for depositing a slurry of fibers dispersed in a liquid medium onto a moving screen of a papermaking machine comprising a substantially horizontal elongated enclosed entrance chamber tapered to a supply orifice which joins a supply means at one extremity thereof and expanded to a rectangular opening at its opposite extremity, said rectangular opening having a cross sectional area of less than about three times the supply orifice cross sectional area, a substantially rectangular exit chamber joined to the said entrance chamber at an upwardly inclined angle of from about 20 to about 45 measured from the horizontal plane of the entrance chamber and having two open opposite sides, two enclosed opposite sides and an enclosed upper and lower face thereto, said exit chamber being joined along one open side thereof to the entrance chamber to permit continuous flow therethrough and having its lower face, which is adapted to be in continuous relationship to the moving screen, fully enclosed from the point of joinder of entrance and exit chamber to at least about /2 of the distance to the opposite open extremity, and a non-round turbulence inducing bar rotatably mounted at its ends within the said exit chamber and positioned between the juncture of the entrance and exit chamber at a point not more than /2 the distance measured along the lower face of said exit chamber, from the extremity of said lower face, and positioned with its long axis substantially parallel to the horizontal plane of the entrance chamber and substantially perpendicular to the plane from the upwardly inclined axis of the exit chamber and the horizontal axis of the entrance chamber.

The term paperrnaking machine is used to designate a Fourdrinier machine or other such conventional papermaking apparatus wherein a slurry is continuously laid down on a moving screen so as to storm a continuous sheet.

The term staple fibers is used to signify fibers or filaments of textile denier which are short in length as opposed to continuous filaments. In general, the lengths of the fibers may vary from a fraction of an inch to several inches. For the present invention, however, it is preferred that the fibers be of from to about -1 inch in length although minor amounts of longer fibers may be substituted in part for the staple fibers herein employed.

The concentration of solids in the slurry should be kept 3,123,520 Patented Mar. 3, 1964 "ice at a value of less than about 0.35% in order to prevent clumping and a corresponding unevenness in the final sheet-like structure. The preferred range of concentration is from about 0.03 to about 0.10%, with the lower concentrations being used for the longer length fibers.

The term turbulent flow is given its conventional meaning, as in hydraulics, to signify that the fio-W is nonviscous or non-laminar.

The liquid which may be used in the practice of the present invention is any liquid which is inert to both the fibers :and the fibrids. Water vfrom an economic standpoint is, of course, preferred, although other inert liquids may also be used.

To be designated a fibrid, a particle must possess (a) an ability to form a waterleaf having a couched wet tenacity of at least about 0.002 gram per denier when a plurality of the said particles is deposited from a liquid suspension upon a screen, which waterleaf, when dried at a temperature below about 50 C., has a dry tenacity at least equal to its couched Wet tenacity and (b) an ability, when a plurality of the said particles is deposited concomitantly with staple fibers from a liquid suspension upon a screen, to bond a substantial weight of the said fibers by physical entwinement of the said particles with the said fibers to give a composite waterleaf with a wet tenacity of at least about 0.002 gram per denier. In addition, fibrid particles have a Canadian freeness number between and 790 and a high absorptive capacity for water, retaining at least 2.0 grams of water per gram of particle under a compression load of about 39 grams per square centimeter. By wholly synthetic polymeric is meant that the fibrid is formed of a polymeric material synthesized by man as distinguished from a polymeric product of nature or derivative thereof.

Any normally solid wholly synthetic polymeric material may be employed in the production of fibrids. By normally solid is meant that the material is non-fluid under normal room conditions. By an ability to bond a substantial weight of (staple) fibers is meant that at least 50% by weight of staple based on total staple and fibrids can be bonded from a concomitantly deposited mixture of staple and fibrids.

It is believed that the fibrid characteristics recited above are a result of the combination of the morphology and non-rigid properties of the particle. The morphology is such that the particle is non-granular and has at least one dimension of minor magnitude relative to its largest dimension, i.e., the fibrid particle is fiber-like or filmlike. Usually, in any mass of fibrids, the individual fibrid particles are not identical in shape and may include both fiber-like and film-like structures. The non-rigid characteristic of the fibrid, which renders it extremely supple in liquid suspension and which permits the physical entwinem ent described above, is presumably due to the presence of the minor dimension. Expressing this dimension in terms of denier, as determined in accordance with the fiber coarseness test described in Tappi 41, A- 7A, N0. 6 (June) 1958, fibrids have a denier no greater than about 15.

Complete dimensions and ranges of dimensions of such heterogeneous and odd-shaped structures are difficult to express. Even screening classifications are not always completely satisfactory to define limitations upon size since at times the individual particles become entangled unease-o with one another or wrap around the wire meshes of the screen and thereby fail to pass through the screen. Such behavior is encountered particularly in the case of fibrids made from soft (i.e., initial modulus below 0.9) polymers. Hard polymers (i.e., initial modulus above 0.9 g./ denier) are more readily tested. As a general rule however, fibrid particles, when classified according to the Clark Classification Test (Tappi, 33, 2948, No. 6 (June) 1950) are retained to the extent of not over on a lO-mesh screen, and retained to the extent of at least 90% on a ZOO-mesh screen.

Fibrid particles are usually frazzled, ha e a high specific surface area and, as indicated, a high absorptive capacity for water.

Preferred fibrids are those the waterleaves of which when dried for a period of twelve hours at a temperature below the stick temperature of the polymer from which they are made (i.e., the minimum temperature at which a sample of the polymer leaves a wet molten trail as it is stroked with a moderate pressure across the smooth surface of a heated block) have a tenacity of at least about 0.005 gram per denier.

Fibrid particles are described in detail and claimed in United States application Serial No. 788,371, now US. Patent No. 2,999,788.

The term synthetic polymer is intended to designate a polymeric material synthesized by man as distinguished from a polymeric product of nature or a derivative thereof.

The present invention provides a headbox for depositing a slurry of fibers dispersed in a liquid medium onto a moving screen of a papermaking machine comprising a substantially horizontal elongated enclosed entrance chamber tapered to a supply orifice which joins a supply means at one extremity thereof and expanded to a rectangular opening at its opposite extremity, said rectangular opening having a cross sectional area of less than about three times the supply orifice cross sectional area, a substantially rectangular exit chamber joined to the said entrance chamber at an upwardly inclined angle of from about 2.0 to about 45 measured from the hori zontal plane of the entrance chamber and having two open opposite sides, t-wo enclosed opposite sides and an enclosed upper and lower face thereto, said exit chamber being joined along one open side thereof to the entrance chamber to permit continuous flow therethrough and having its lower face, which is adapted to be in continuous relationship to the moving screen, fully enclosed from the point of joinder of entrance and exit chamber to at least about /2 of the distance to the opposite open extremity, and a non-round turbulence inducing bar rotatably mounted at its ends within the said exit chamber and positioned between the juncture of the entrance and exit chamber at a point not more than /2 the distance measured along the lower face of said exit chamber, from the extremity of said lower face, and positioned with its long axis substantially parallel to the horizontal plane of the entrance chamber and substantially perpendicular to the plane from the upwardly inclined axis of the exit chamber and the horizontal axis of the entrance chamber.

By the term substantially horizontal is meant that the direction of flow of a liquid passing through the entrance chamber is principally in the horizontal direction.

The terminology with a cross sectional area of less than about three times the supply orifice cross sectional area is used to signify that the entrance chamber is not appreciably greater in cross sectional area than the cross ectional area of the supply orifice. It is preferred, that the entrance chamber cross sectional area be larger than that of the supply orifice in order to decrease the velocity of the liquid flowing through the entrance chamber. By so regulating the cross sectional area, the liquid re mains in turbulent flow and the slurry does not tend to clump or settle out.

The invention will be more readily understood by reference to the drawings.

FIGURE 1 is a flow sheet diagraming a continuous process for producing a sheet in which a suspension containing a. mixture of staple and fibrid is deposited on a Fourdrinier machine. I

FIGURE 2 illustrates diagrammatically the process of FIGURE 1, identifying the equipment and the principal parts of the Fourdrinier machine as discussed more in detail hereinafter.

FIGURE 3 is a diagrammatic representation of the headbox 13 of the present invention which is shown on the Fourdrinier machine in FIGURE 2.

FTG'URES 4 and 5 show the non-round turbulence bar with hexagonal and octagonal cross sections, respectively.

Typical processes wherein papermaking machinery may be used in producing sheet products from fibrids are illustrated in FIGURES 1 and 2. As mentioned previously, FIGURE 1 is a flow sheet showing a suitable commercial system wherein a slurry of fibrids is fed from Fibrid Supply through a Refiner into a Stock Tank. The staple is slurried with water in another stock tank or in a slurrying device such as a Hydrapulper. At the first Mixer the two slurries are brought together in a region of high velocity, intense turbulence, and low holdup volume such as in a pipe T. Following the first Mixer, the mixture may be dilu ed further and broke added in a second Mixer. The second Mixer then feeds the Fourdrinier Machine wherein the waterleaf is laid down, progressing thereafter through the Wet Press," the Dryer Rolls, the Calender and finally to the Product Reel. The Broke, i.e., collection of scraps in various stages of dryness, is fed through a Slusher for recycling to the second Mixer.

FIGURE 2 is a diagrammatic representation of the flow sheet showing a supply of suspending liquid 1, feeding fibrid mixing vessel 2 through valve 3 and the staple suspending vessel 4 through valve 5. Each vessel is supplied with an agitator 6. A supply of fibrid is fed to vessel 2 from a fibrid cake 7. A supply of yarn 8 is fed through cutter h into staple suspending vessel 4 or alternatively pre-cut staple fibers are metered from a bale. The slurries in each of the suspending vessels are pumped by pumps It? into mixing T 11, the fibrid slurry optionally passing through a refiner 12. The pumps used for the fiber slurry should be of a type which does not generate foam and does not tend to clog. A suitable pump is, for example, the Vanton FleX-i-liner (made by the Vanton Pump Company of Hillside, N1), which is an eccentric rotor pump with no rotating or oscillating parts in contact with the liquid. Also suitable is the Ingersoll Rand centrifugal pump having an 'Egger closed impeller, or other centrifugal pumps of similar design. The fibrid pump may be of any conventional design. The mixed slurry then flows through a headbox 13 and onto moving screen 14, the water passing through the said screen and being removed in part by table rolls 15 and suction boxes 15'. As the screen reaches couch roll 16, a Water-leaf 17 of the suspended solids has formed. The screen 14 being continuous passes back over stretch roll 18 and breast roll 19. Waterleaf 17 passes under fly roll 20, bet-ween wet press rolls 21, over guide roll 22 to a series of dryer rolls 23', to a calender stack 24 and finally to a windup reel 25. A sheet containing only a low proportion of fibrids may tend to delaminate as it passes under the wet process roll 21 in such a way that fibers are pulled up from the surface of the sheet and, in some cases, even adhere to the surface of the Wet press roll 21. This difiiculty can be minimized by using a press roll with a low friction surface, for instance a roll coated with polytetrafiuoroethyle-ne.

FIGURE 3 is a diagrammatic representation of the headbox 13 of the present invention which is shown on the Fourdrinier machine in FIGURE 2. The supply orifice 26 supplies the slurry to the entrance chamber 27 which in turn supplies it to the exit chamber 28. A rotating non-round turbulence inducing bar 29 in the exit chamber 28 maintains the slurry in turbulent flow until the sheet-like structure 35 is deposited on moving screen 34 as it passes bet-ween the stretch roll 32 and breast roll 33. The screen may be supported along its inclined portion by the use of open-faced rolls. such as conventional dandy rolls. The upper face of the exit chamber 28 is enclosed. The lower face of the exit chamber is open down to the forward lip 31 which rests against the moving screen 34. The liquid level 36 is maintained above the forward lip 31 so as to deposit the solids from the slurry onto the moving screen 34. A flexible film 30 is draped from the top portion of the headbox onto the liquid level 36 so as to eliminate the free surface of the slurry. The flexible film 30 may be held below the liquid level 36 by means of a rod (not shown) passing through the headbox. The flexible film 30 causes a uniform sheetlike structure 35 to be formed on moving screen 34. The angle A is maintained between about 20 and about 45 for optimum quality sheet formation. For very small angle A, the force of the incoming slurry passing over the top of the newly-deposited, half-formed sheet causes masses of fiber to be picked up from one spot on the sheet and deposited elsewhere. The result is an inhomogeneous sheet having unacceptable thick and thin spots. In addition for small angle A the properties of the sheet are highly directional which may be undesirable. In order to avoid these difi'iculties, in the process of this invention the angle A should be at least about 20-". It is preferable that angle A be less than about 45 in order to avoid irregularities in the sheet structure due to sliding back of the newly-deposited, slushy material. Slide-back is especially noticeable at the point Where the sheet structure breaks the surface of the slurry. It can be minimized by applying suction at the point at which the sheet emerges from the slurry. It can also be reduced by bringing the level of the slurry up onto the nearly-horizontal portion of the wire. (This portion of the wire will not actually be horizontal, but will be tilted rearwardly at a slight angle, which is usually less than about 3.)

The headbox is provided with a turbulence inducing rotatable non-round bar to promote a controlled turbulence in the slurry. The said bar must be positioned within the headbox across the flow of the slurry, yet in a position before the point where deposition on the moving screen takes place so that turbulence is not present when deposition occurs. The exact position of the bar will vary depending on the size of the headbox and the volume of the slurry. Uncontrolled turbulence at the point of deposition would result in a non-uniform sheet due to uneven deposition. Preferably the turbulence inducing bar is positioned at the juncture of the horizontal entrance chamber with the upwardly inclined exit chamber and would be of rectangular, hexagonal or octagonal cross section.

The position of the turbulence bar, with relation to the point of deposition on the moving screen, is very important since unless the bar is positioned a sufficient distance from the point of deposition to allow a substantial reduction of turbulence, the sheet deposited on the screen will not be characterized by uniformity of thickness but will exhibit thick and thin areas resulting from the clumping or bunching of fibers just prior to deposition. When the turbulence is substantially reduced, just prior to deposition, the fibers in suspension remain in their thoroughly intermixed state and are, therefore, evenly deposited on the screen since there are no channels or eddy currents present which would cause the bunching or clumping of fibers.

Headbox Construction A headbox is constructed according to FIGURE 3 having the following approximate dimensions (with the upper side of the entrance chamber being horizontal).

Entrance chamber 27:

Supply orifice (pipe) 3 sq. inches.

Length 36 inches.

Opening at exit chamber 12" x A2".

Exit chamber 28:

Vertical height (above horizontal) 12 inches.

Width (across the sheet) 12 inches.

Depth (perpendicular to moving screen) 2 inches.

Forward lip length 2 /2 inches. Angle A 45 degrees. Turbulence inducing bar 29:

Shape Hexagonal.

Outer diameter 1 /2 inches.

Flexible film 30:

Polyethylene film.

The headbox of the Fourdrinier is replaced by the modified headbox above-described. The moving screen of the machine is adjusted to move at an angle of 45 with the horizontal so that it corresponds to the open face of the headbox. The breast roll 33, which is normally a solid roll, is replaced with a 6-inch open roll of dandy roll construction. Inflatable flexible tubing (rubber) is used around the open face of the headbox to form a seal with the moving screen and prevent leakage.

In a preferred embodiment of the invention each element of fiber-fibrid slurry is deposited on the moving screen within about 15 seconds after its formation. This is preferably done by mixing the fibers and fibrids continuously in a mixing tee and, as soon as possible thereafter, depositing the slurry on the moving screen. By holding each element or portion of the fiber-fibrid slurry to a lifetime of less than about 15 seconds, flocculation problems are substantially avoided.

In another preferred embodiment, the staple fibers are dispersed using a wetting agent which results in a uniform dispersion being formed and consequently uniform sheet-like structures. The wetting agent may be added directly to the dispersion of fibers, or the fibers may be coated with the wetting agent prior to the formation of the dispersion. When using synthetic fibers this is conveniently accomplished by leading the tow through a solution of the wetting agent prior to the tow being cut into staple. In general, the conditions should be so regulated that the final slurry contains only a few percent of the wetting agent (based on the weight of the staple fibers). When a non-ionic wetting agent is employed about 0.5 to about 1.0% of the wetting agent is sufficient to obtain good results. A cationic wetting agent, however, requires from about 3 to about 5% to accomplish the same results and the non-ionic wetting agent is preferred.

When such coated fibers are dispersed no prohibitive additional expense is incurred because of the very small amounts of hydrophilic agents applied. These agents also tend to minimze the formation of objectionable foam. The proper selection of agitators, pumps, dilution water entrances, etc., are all designed or chosen with this in mind. In some instances deaeration of the slurries, particularly the fiber slurry, is also desired to prevent foaming. If the fibers are properly cut, with no fused or long ends, gentle agitation will be sufficient to produce a uniform suspension of the fibers in water, particularly if they are dropped gradually onto the surface of the gently agitated water. The coatings are retained on the surface of the fibers suificiently well to permit redispersion of the fibers, even after they have been processed into papers or sheets. This is particularly advantageous in the reprocessing of broke. I

Another advantage derived from the use of properly cut, hydrophilically-coated fibers is the ease and simplicity of continuous processing. Water and fibers may be continuously metered (by the cutter or other suitable staple metering devices) in the desired proportion to the dispersing tank. Dwell time in the tank need only be long enough to assure uniform dispersion (not more than 3 to 5 minutes). A minimum of mechanical work is thus required to produce a smooth and uniform dispersion and an economical advantage of low stock chest capacity is realized.

The sheet-like products produced according to this invention vary from a paper-like sheet to sheets having leather-like qualities. In gene 'al, the soft polymer fibrids produce sheets having a fabric-like drape and a pleasing soft hand similar to that of suede, leather, or chamois whereas the hard polymer fibrids tend to produce a harder finish and hand. As the amount of staple fibers in the fibrid sheet increases it tends to produce stiffer and stronger sheets. The sheet properties may also be modified by mixing both soft and hard polymer fibrids or by blending cellulosic pulps into the fibrid slurry.

The properties of the sheet-like structures may also be modified by increasing the speed of the moving screen and by increasing the amount of vacuum used to deposit the slurry. As the speed of the moving screen is increased less of the solids from the slurry are deposited and a thin paper-like product results. With a slower moving screen the solids tend to build up and a thicker sheet is produced. By controlling the vacuum on the papermaking machine the compactness as well as the thickness may be varied. Thus, when a higher vacuum is used the sheet-like structure tends to be more compact and less porous.

Another method of controlling the type of product produced is by calendering the sheet prior to or after its removal from the machine. By using heat and pressure the fibrids may be fused partially or completely into a solid mass. This may also be accomplished in the absence of pressure by using infrared panels or the like. While the structure of the fibrid is generally lost in such an operation, the resulting product is of quite high strength which is probably due to the uniform distribu tion of the fibers in the polymer.

The sheet-like products of the present invention may be used in a variety of ways depending on the various modifications used to produce these products. The thin paper-like sheets may be used as paper for such applications such as maps, blueprints, and packaging materials for use in humid climates. The thicker products are useful as non-woven fabrics, felts, synthetic leather, tarpaulins, tentage materials, cardboards and other sheet structures having a great range in basis weights and a great variety of composition.

Many equivalent modifications will be apparent to those skilled in the art from a reading of the above Without a departure from the inventive concept.

This application is a continuation-in-part of the United States application Serial No. 676,013, filed August 2, 1957, now abandoned.

What is claimed is:

1. A headbox for depositing a slurry of fibers dispersed in a liquid medium onto a moving screen of a papermaking machine comprising a substantially horizontal elongated enclosed entrance chamber tapered to a supply orifice which joins a supply means at one extremity thereof and expanded to a rectangular opening at its opposite extremity, said rectangular opening having a cross sectional area of less than about three times the supply orifice cross-sectional area, a substantially rectangular exit chamber joined to the said entrance chamber at an upwardly inclined angle of from about 20 to about 45 measured from the horizontal plane of the entrance chamber and having two open opposite sides, two enclosed opposite sides and an enclosed upper and lower face thereto, said exit chamber being joined along one open side thereof to the entrance chamber to permit continuous flow therethrough and having its lower face, which is adapted to in continuous relationship to the moving screen, fully enclosed from the point of joinder of entrance and exit chamber to at least about /2 of the distance to the opposite open extremity, and wherein a flexible sheet is attached along the upper face of the said exit chamber at the extremity opposite the said upper face which joins the supply chamber of sufficient length to allow it to drape down to rest on the surface of the water inside the headbox and to then extend a distance up along the moving screen in the direction of movement of said screen to a point where it is freely forward and will rest 011 the forward substantially horizontal portion of the said moving screen, and a non-round turbulence inducing bar rotatably mounted at its ends Within the said exit chamber and positioned between the juncture of the entrance and exit chamber at a point not more than /2 the dis- Lance measured along the lower face of said exit chamher, from the extremity of said lower face, and positioned with its long axis substantially parallel to the horizontal plane of the entrance chamber and substantially perpendicular to the plane from the upwardly inclined axis of the exit chamber and the horizontal axis of the entrance chamber.

2. An improved headbox unit for receiving, controlling, and conveying a moving stream of a liquid slurry into contact with a moving screen conveyor to form a non-woven shcet-like structure on said conveyor, said unit comprising in combination; a first conduit portion having an outlet end, and. an inlet end with an opening for receiving a moving stream of a liquid slurry contain ing fibrous elements from a supply source, said first conduit portion constructed and arranged to control the stream of slurry received and distribute said slurry so that it achieves a predetermined increased width and a predetermined reduced thickness at the outlet end of said first conduit portion, said headbox unit further comprising a second conduit portion operatively joined to said outlet end of said first conduit portion and extending along a portion of a moving screen conveyor, said second conduit portion provided with a discharge opening aligned with a transverse section of the said portion of said moving screen conveyor so that moving slurry received from said first conduit portion is conducted into engagement with one side of said portion of said screen conveyor a movable uniform polygonal bar agitator means mounted for engagement with the stream of slurry in said unit and positioned transversely to the direction of slurry movement at a point spaced a given distance away from said discharge opening to maintain the stream of slurry in a condition of turbulence so that the fibrous elements are thoroughly intermixed and evenly distributed throughout the slurry, the spacing of said point from said discharge opening determined such that, for the speed of movement of said slurry stream, and the speed of movement of the screen conveyor, the spacing is sufiiciently large so that the turbulence of the slurry is substantially eliminated by the time the slurry reaches the discharge opening and screen conveyor, yet at the same time sufficiently small so that the slurry is evenly conducted into engagement with the screen conveyor before the fibrous elements can settle out, form clumps, or become unevenly distributed due to the reduced turbulence near the discharge opening.

3. The improved unit of claim 2 in which the path of movement of said screen conveyor adjacent the discharge opening is positioned at an angle of about 20 to about from the horizontal.

4. The improved unit of claim 3 in which said moving agitator means comprises a driven rotary elongated memher having an uniform polygonal transverse cross section along its length.

5. The improved unit of claim 4 in which said second conduit portion of said unit comprises a flexible means mounted therein in contact with the upper surface of the slurry adjacent said discharge opening and in cont ct with a portion of the formed structure on the screen conveyor to control the surface of the slurry to prevent free surface action during formation of the sheet-like structure.

6. The improved unit of claim 4 in which said first conduit portion extends in a substantially horizontal direction and varies in transverse cross section from a substantially circular inlet end opening to a Wide thin outlet end cross section, said second conduit portion being fitted and operatively connected to said outlet end and extending therefrom in a direction substantially parallel to the path of movement of said screen conveyor adjacent said discahrge opening, the outlet end of the first conduit portion having a transverse cross section less than 3 times that of the inlet end opening of said first conduit portion.

References Cited in the file of this patent UNITED STATES PATENTS Mickle Apr. 22, Upson Apr. 2, Fletcher Aug. 26, Osborne June 23, Rosmait May 4, BidWell Nov. 22, Boone et a1. Apr. 29, Mueller June 9, Goumeniouk July 14,

FOREIGN PATENTS Great Britain Aug. 12, 

2. AN IMPROVED HEADBOX UNIT FOR RECEIVING, CONTROLLING, AND CONVEYING A MOVING STREAM OF A LIQUID SLURRY INTO CONTACT WITH A MOVING SCREEN CONVEYOR TO FORM A NON-WOVEN SHEET-LIKE STRUCTURE ON SAID CONVEYOR, SAID UNIT COMPRISING IN COMBINATION; A FIRST CONDUIT PORTION HAVING AN OUTLET END, AND AN INLET END WITH AN OPENING FOR RECEIVING A MOVING STREAM OF A LIQUID SLURRY CONTAINING FIBROUS ELEMENTS FROM A SUPPLY SOURCE, SAID FIRST CONDUIT PORTION CONSTRUCTED AND ARRANGED TO CONTROL THE STREAM OF SLURRY RECEIVED AND DISTRIBUTE SAID SLURRY SO THAT IT ACHIEVES A PREDETERMINED INCREASED WIDTH AND A PREDETERMINED REDUCED THICKNESS AT THE OUTLET END OF SAID FIRST CONDUIT PORTION, SAID HEADBOX UNIT FURTHER COMPRISING A SECOND CONDUIT PORTION OPERATIVELY JOINED TO SAID OUTLET END OF SAID FIRST CONDUIT PORTION AND EXTENDING ALONG A PORTION OF A MOVING SCREEN CONVEYOR, SAID SECOND CONDUIT PORTION PROVIDED WITH A DISCHARGE OPENING ALIGNED WITH A TRANSVERSE SECTION OF THE SAID PORTION OF SAID MOVING SCREEN CONVEYOR SO THAT MOVING SLURRY RECEIVED FROM SAID FIRST CONDUIT PORTION IS CONDUCTED INTO ENGAGEMENT WITH ONE SIDE OF SAID PORTION OF SAID SCREEN CONVEYOR A MOVABLE UNIFORM POLYGONAL BAR AGITATOR MEANS MOUNTED FOR ENGAGEMENT WITH THE STREAM OF SLURRY IN SAID UNIT AND POSITIONED TRANSVERSELY TO THE DIRECTION OF SLURRY MOVEMENT AT A POINT SPACED A GIVEN DISTANCE AWAY FROM SAID DISCHARGE OPENING TO MAINTAIN THE STREAM OF SLURRY IN A CONDITION OF TURBULENCE SO THAT THE FIBROUS ELEMENTS ARE THOROUGHLY INTERMIXED AND EVENLY DISTRIBUTED THROUGHOUT THE SLURRY, THE SPACING OF SAID POINT FROM SAID DISCHARGE OPENING DETERMINED SUCH THAT, FOR THE SPEED OF MOVEMENT OF SAID SLURRY STREAM, AND THE SPEED OF MOVEMENT OF THE SCREEN CONVEYOR, THE SPACING IS SUFFICIENTLY LARGE SO THAT THE TURBULENCE OF THE SLURRY IS SUBSTANTIALLY ELIMINATED BY THE TIME THE SLURRY REACHES THE DISCHARGE OPENING AND SCREEN CONVEYOR, YET AT THE SAME TIME SUFFICIENTLY SMALL SO THAT THE SLURRY IS EVENLY CONDUCTED INTO ENGAGEMENT WITH THE SCREEN CONVEYOR BEFORE THE FIBROUS ELEMENTS CAN SETTLE OUT, FORM CLUMPS, OR BECOME UNEVENLY DISTRIBUTED DUE TO THE REDUCED TURBULENCE NEAR THE DISCHARGE OPENING. 